Its a pretty good army-staff. You can summon an unlimited amount of Tree Spirits, a lot of Undead Zombies, an unlimited amount of Elementals and the Death himself (if you want to suicide ;) ), and all of them will fight for you, while you can hide yourself in a shield. It does take some time to build up an army, and you will have to repeat it every time you go to the next map-part, but you will never die. The immunity to poison is only helpfull in chapter 9 against the undead, but its still a really good staff if you use it correctly and with the right strategie.